User profiles

(Written by Paul Cobbaut, https://github.com/paulcobbaut/, with contributions by: Alex M. Schapelle, https://github.com/zero-pytagoras/)

Logged on users have a number of preset (and customized) aliases, variables, and functions, but where do they come from ? The shell uses a number of startup files that are executed (or rather sourced) whenever the shell is invoked. What follows is an overview of startup scripts.

system profile

Both the bash and the ksh shell will verify the existence of /etc/profile and source it if it exists.

When reading this script, you will notice (both on Debian and on Red Hat Enterprise Linux) that it builds the PATH environment variable (among others). The script might also change the PS1 variable, set the HOSTNAME and execute even more scripts like /etc/inputrc

This screenshot uses grep to show PATH manipulation in /etc/profile on Debian.

root@linux:~# grep PATH /etc/profile
  PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
  PATH="/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games"
export PATH
root@linux:~#

This screenshot uses grep to show PATH manipulation in /etc/profile on RHEL7/CentOS7.

[root@linux ~]# grep PATH /etc/profile
    case ":${PATH}:" in
                PATH=$PATH:$1
                PATH=$1:$PATH
export PATH USER LOGNAME MAIL HOSTNAME HISTSIZE HISTCONTROL
[root@linux ~]#

The root user can use this script to set aliases, functions, and variables for every user on the system.

~/.bash_profile

When this file exists in the home directory, then bash will source it. On Debian Linux 5/6/7 this file does not exist by default.

RHEL7/CentOS7 uses a small ~/.bash_profile where it checks for the existence of ~/.bashrc and then sources it. It also adds $HOME/bin to the $PATH variable.

[root@linux ~]# cat /home/paul/.bash_profile
# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/.local/bin:$HOME/bin

export PATH
[root@linux ~]#

~/.bash_login

When .bash_profile does not exist, then bash will check for ~/.bash_login and source it.

Neither Debian nor Red Hat have this file by default.

~/.profile

When neither ~/.bash_profile and ~/.bash_login exist, then bash will verify the existence of ~/.profile and execute it. This file does not exist by default on Red Hat.

On Debian this script can execute ~/.bashrc and will add $HOME/bin to the $PATH variable.

root@linux:~# tail -11 /home/paul/.profile
if [ -n "$BASH_VERSION" ]; then
    # include .bashrc if it exists
    if [ -f "$HOME/.bashrc" ]; then
        . "$HOME/.bashrc"
    fi
fi

# set PATH so it includes user's private bin if it exists
if [ -d "$HOME/bin" ] ; then
    PATH="$HOME/bin:$PATH"
fi

RHEL/CentOS does not have this file by default.

~/.bashrc

The ~/.bashrc script is often sourced by other scripts. Let us take a look at what it does by default.

Red Hat uses a very simple ~/.bashrc, checking for /etc/bashrc and sourcing it. It also leaves room for custom aliases and functions.

[root@linux ~]# cat /home/paul/.bashrc
# .bashrc

# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi

# Uncomment the following line if you don't like systemctl's auto-paging feature:
# export SYSTEMD_PAGER=

# User specific aliases and functions

On Debian this script is quite a bit longer and configures $PS1, some history variables and a number af active and inactive aliases.

root@linux:~# wc -l /home/paul/.bashrc
110 /home/paul/.bashrc

~/.bash_logout

When exiting bash, it can execute ~/.bash_logout.

Debian use this opportunity to clear the console screen.

serena@linux:~$ cat .bash_logout
# ~/.bash_logout: executed by bash(1) when login shell exits.

# when leaving the console clear the screen to increase privacy

if [ "$SHLVL" = 1 ]; then
    [ -x /usr/bin/clear_console ] && /usr/bin/clear_console -q
fi

Red Hat Enterprise Linux 5 will simple call the /usr/bin/clear command in this script.

[serena@linux ~]$ cat .bash_logout 
# ~/.bash_logout

/usr/bin/clear

Red Hat Enterprise Linux 6 and 7 create this file, but leave it empty (except for a comment).

student@linux:~$ cat .bash_logout
# ~/.bash_logout

Debian overview

Below is a table overview of when Debian is running any of these bash startup scripts.

script su su - ssh gdm

~./bashrc no yes yes yes

~/.profile no yes yes yes

/etc/profile no yes yes yes

/etc/bash.bashrc yes no no yes

: Debian User Environment

RHEL5 overview

Below is a table overview of when Red Hat Enterprise Linux 5 is running any of these bash startup scripts.

script su su - ssh gdm

~./bashrc yes yes yes yes

~/.bash_profile no yes yes yes

/etc/profile no yes yes yes

/etc/bashrc yes yes yes yes

: Red Hat User Environment

practice: user profiles

Make a list of all the profile files on your system.
Read the contents of each of these, often they source extra scripts.
Put a unique variable, alias and function in each of those files.
Try several different ways to obtain a shell (su, su -, ssh, tmux, gnome-terminal, Ctrl-alt-F1, ...) and verify which of your custom variables, aliases and function are present in your environment.
Do you also know the order in which they are executed?
When an application depends on a setting in $HOME/.profile, does it matter whether $HOME/.bash_profile exists or not?

solution: user profiles

Make a list of all the profile files on your system.
```
ls -a ~ ; ls -l /etc/pro* /etc/bash*
```
Read the contents of each of these, often they source extra scripts.
Put a unique variable, alias and function in each of those files.
Try several different ways to obtain a shell (su, su -, ssh, tmux, gnome-terminal, Ctrl-alt-F1, ...) and verify which of your custom variables, aliases and function are present in your environment.
Do you also know the order in which they are executed?

Same name aliases, functions and variables will overwrite each other
When an application depends on a setting in $HOME/.profile, does it matter whether $HOME/.bash_profile exists or not?

Yes it does matter. (man bash /INVOCATION)